Draft guidelines released by the National Institutes of Health reflect rules with broad congressional support, excluding more controversial sources such as cells derived from embryos created just for experiments.
"We think this will be a huge boost for the science," said Acting NIH Director Raynard Kington. "This was the right policy for the agency at this point in time."
The limit will disappoint some researchers who wanted to use a broader variety of cells. But it still means that perhaps hundreds more stem cell lines will be available for government-funded study soon.
"Some groups and scientists have wanted the administration to go further. But we are happy to have this progress after such a long period of limited opportunities to pursue this very important line of research," said Alan Leshner of the American Association for the Advancement of Science.
The guidelines are "a reasonable compromise based on where the science stands now," said Dr. Sean Morrison, director of the University of Michigan Center for Stem Cell Biology. "We may need to revisit some of the details down the road depending on how the science develops."
Scientists are trying to harness embryonic stem cells - master cells that can morph into any cell of the body
- to one day create replacement tissues and better treat, possibly even cure, ailments ranging from diabetes to Parkinson's to spinal cord injury.
Culling those stem cells - which can propagate indefinitely in lab dishes
- destroys a days-old embryo, a result strongly opposed by many on moral grounds. So the Bush administration had limited taxpayer-supported research to a small number of embryonic stem cell "lines" or groups already in existence as of August 2001.
Last month, Obama lifted that restriction, widening the field. But he left it to the NIH to set ethics guidelines determining which cell lines now will qualify for government funding.
Federal law forbids using taxpayer money to create or destroy an embryo. At issue here are rules for working with cells that initially were created using private money.
Many scientists had hoped the guidelines would allow use of stem cells derived from embryos created just for science, perhaps even using cloning techniques that could make them genetically customized for a potential recipient.